Bioactive Form of Vitamin K2 10X Better Absorbed Than K1, From Spinach Promotes Bones Health 90 Micrograms Dietary Supplement Jarrow Formulas MK-7 is made via fermentation by Bacillus subtilis subsp. natto. MK-7 (menaquinone-7) is the bioactive form of vitamin K2, traditionally found naturally occurring in Natto. MK-7 is ten times better absorbed than K1, from spinach and is responsible for the carboxylation of specific bone proteins needed for building bones.